1. Field of the Invention
The present invention relates to a control of an engine in a vehicle equipped with an automatic transmission and, more particularly, to a control of output torque of the engine in coordination with change-over of speed stages of the automatic transmission in a manner that the output torque of the engine is temporarily reduced during the change-over of speed stages and is recovered toward the completion of the change-over of the speed stages.
2. Description of the Prior Art
It is already known to reduce output torque of the engine which drives the wheels in a vehicle via an automatic transmission temporarily during changing over of the speed stages of the transmission in order to reduce a shock which is caused by the change-over of gear trains, as proposed in British Patent 929621, German Patent or Publication 1080415, 1480177 or 1626427, French Patent 1524354, German Patent Publications 2109620, 2163979 and 2805544 acknowledged in Japanese Patent Laying-open Publication 55-46095 based upon German Patent Application P2842389. In view of the nature of abruptly reducing and recovering engine output torque according to such acknowledged various prior arts it is proposed in said Japanese Publication 55-46095 to gradually reduce and recover engine output torque for a change-over of speed stages of the automatic transmission according to a predetermined pattern of sloping down and up. On the other hand it is also known to monitor the rotational speed of a rotary member in an automatic transmission to detect a time point close to the completion of a change-over of speed stages of the automatic transmission, as described in Japanese Patent Laying-open Publication 60-260749 in which the rate of change of rotational speed of such a rotary member is monitored to detect such a time point at which the rate has decreased to a certain small limit value so as thereby to start the recovery of the temporarily reduced engine torque according to a gradually proceeding manner by taking a predetermined period.
However, it is a time point generally very close to the completion of a change-over of speed stages that the value of the rate of change of rotational speed of a rotary member in the transmission approaches zero, and such a time point is generally too late to start a gradual recovery of engine output torque temporarily reduced for a change-over of speed stages. Further, the shape of performance curve which represents the variation of rotational speed of a rotary member such as the input rotary member of the transmission which, in an upshifting from a certain first speed stage to a certain second speed stage, changes its rotational speed from a rotational speed corresponding to a multiplication of the rotational speed of the output rotary member of the transmission times a gear ratio of said certain first speed stage to a rotational speed corresponding to a multiplication of the rotational speed of the output rotary member times a gear ratio of said certain second speed stage, fluctuates substantially according to fluctuations in the operational conditions of the friction engaging means which is engaged for setting up the speed stage posterior to the changer-over of speed stages, i.e. said certain second speed stage, and therefore, when it is so adapted that the temporarily reduced engine output torque is recovered according to a predetermined time schedule in a final stage of the change-over of speed stages, the recovery of the reduced engine output torque is not satisfactorily synchronized with the completion of the change-over of speed stages, thereby inducing generation of an undesirably high shock.